It has been generally known in the network systems field how to provide redundant capabilities. Redundant packet forwarding devices are especially useful to handle the possibility of failed links and/or failed packet forwarding devices (e.g. switches, routers, bridges). However, the detection of network topology loops and the utilization of redundant paths is problematic, particularly in view of the time involved in detecting the path and rerouting traffic. Further, protocols which have been used are complicated to configure and manage.
Traditionally the spanning tree protocol has been use to provide both Layer 1 and 2 redundancy, in switch networks, by configuring alternate paths. When a link or switch element fails, a backup link is activated. The spanning tree algorithm defines the active and backup links in the topology. Spanning tree is designed to control the many switches of the topology and has a slow (in the tens of seconds) reconfiguration time.
Spanning tree has a significant disadvantage as to the reconfiguration time. As network systems become more complex and handle additional traffic, the reconfiguration time becomes increasingly problematic. Further, spanning tree disables the redundant path. This negates the possibility of using redundant paths for increases in throughput.
U.S. patent application Ser. No. 09/014,547, filed Jan. 28, 1998 (which is hereby incorporated by reference), discloses trunk clusters, namely a packet based high speed mesh which is formed of a set of loosely coupled switches, a configuration protocol and trunked network interfaces. Each switch, in a trunk cluster, provides a single "shared LAN" by interconnecting two or more links. The attached edge devices run the trunk configuration protocol and view the trunk ports as if they are connected to a shared LAN with multiple other attached devices. The maximum throughput of the trunk cluster increases with each additional switch.
Such a trunk cluster provides significant advantages including layer 1 and layer 2 redundancy, the avoidance of the spanning tree and the ability to provide additional throughput as needed (by adding additional switches to the switch cluster). The provision of such a trunk cluster necessitates further consideration such as further interconnection, interconnecting different trunk clusters or group of trunk clusters.
A scalable switch set is disclosed in U.S. patent application Ser. No. 09/014,548. This provides a redundant switch set based on trunk connections between individual switches of the switch set.